[wasm] Implement correct 2-level namespace for imports.

src/wasm/module-decoder.cc

Index: src/wasm/module-decoder.cc
diff --git a/src/wasm/module-decoder.cc b/src/wasm/module-decoder.cc
index af3a3f666a45dd0dc5423b5aa2783c9c819eaa14..fb8087da14e8ca60f691819926a582edd866780d 100644
--- a/src/wasm/module-decoder.cc
+++ b/src/wasm/module-decoder.cc
@@ -280,9 +280,6 @@ class ModuleDecoder : public Decoder {
         const byte* pos = pc_;
         import->module_name_offset =
             consume_string(&import->module_name_length, true);
-        if (import->module_name_length == 0) {
-          error(pos, "import module name cannot be NULL");
-        }
         import->field_name_offset =
             consume_string(&import->field_name_length, true);